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Slide Rules

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Slide rules were sometimes distinctive by the materials from which they were made. Early rules were often made from boxwood and other woods. By the late 19th century, German manufacturers and Keuffel & Esser of New York City had not only switched to the more uniform and durable mahogany but were also coating the wood with early forms of plastic (celluloid). Around the turn of the 20th century, Japanese firms used bamboo, which did not expand and shrink as much as wood, thus reducing errors in the results of calculations. Later, Pickett slide rules were notable for their aluminum construction and proprietary yellow color. Although the rules tended to be less affordable and popular than wooden rules, manufacturers have used brass and other metals throughout the history of slide rules. Plastic and paper became increasingly widespread for inexpensive rules in the 20th century.

In 1874 F. M. Stapff submitted this model to the U.S. Patent Office. He designed the instrument to calculate the volume of spaces shaped as prisms, such as embankments and ditches. It consists of a wooden base with two slides, one atop the other. The lower slide has pieces of paper pasted on both sides, containing various curves related to finding the equivalent heights of an embankment (e.g., the height of an embankment of the same volume having trapezoidal sides).

The upper slide has five scales on it, numbered from 3 to 7. The upper part of the base has two scales, numbered 1 and 2. The lower part of the base has a scale numbered 8. Scales 1, 2, 3, and 6 are linear. Scales 4, 5, 7, and 8 are logarithmic. A single brass indicator is in a groove between scales 1 and 2; two smaller brass indicators are in a groove below scale 8. A wooden piece at the left end of the rule and a brass piece at the right end of the slide, with a sliding screw and sharp point, have screws for adjusting the rule. See the patent for a detailed account of the use of the instrument.

The lower part of the base is marked: F.M.STAPFF ESTIMATOR. A loose brass piece with the device may be set on "6 PT. Ct." or 7 PT. Ct." It is not mentioned in the patent. There is also a brown leather case that fastens with two straps and buckles. It is marked in Gothic lettering: F. M. Stapff's (/) Estimator.

Fredric Maurice Stapff (or Friedrich Moritz Stapff, 1836–1895) was a German-born geologist and mining engineer who studied at the University of Freiburg and obtained his Ph.D. from Jena in 1861. Stapff worked for a time in Sweden and in the United States, as well as in Germany and Switzerland. He also carried out extensive field work in East Africa, where he died while prospecting for gold. An example of Stapff's estimator was included among the slide rules exhibited at the Science Museum in South Kensington at the Special Loan Collection of Scientific Apparatus in 1876. According to the exhibit catalog, Stapff also patented his estimator in Sweden.

References: Fredric Maurice Stapff, "Improvement in Philosophical Instruments or Estimators" (U.S. Patent 157,239 issued November 24, 1874); "Improved Estimator," Scientific American n.s., 32, no. 2 (January 9, 1875): 25; South Kensington Museum, Handbook to the Special Loan Collection of Scientific Apparatus (Piccadilly: Chapman and Hall, 1876), 30; South Kensington Museum, Catalogue of the Special Loan Collection of Scientific Apparatus, 3rd ed. (London: George Eyre and William Spottiswoode, 1877), 2; Mary Gunn and L. E. W. Codd, Botanical Exploration of Southern Africa: an illustrated history of early botanical literature on the Cape flora : biographical accounts of the leading plant collectors and their activities in southern Africa from the days of the East India Company until modern times (Cape Town: CRC Press, 1981), 332.

This is the U.S. patent model for a cylindrical slide rule invented by George Fuller (1829–1907), a British civil engineer and professor of engineering at Queen's College, Belfast. Fuller received patents in Great Britain (no. 1044) in 1878 and in the United States in 1879. W. F. Stanley of London manufactured the rule from 1879 until 1975, and it was marketed in the United States by Keuffel & Esser, Dietzgen, and other dealers.

The model has a wooden handle and shaft, with a wooden cylinder that slides up and down the shaft. A paper covered with scales fits around the cylinder. The lower edge of the cylinder has a scale of equal parts. The remainder bears a spiral scale divided logarithmically. A rectangular clear plastic pointer has broken from its attachment on the handle and is tucked into a red ribbon tied around the cylinder. A paper patent tag is marked: No. 291.246; 1879 (/) G. Fuller. (/) Calculators. (/) Patented Sept 2. (/) 1879. A printed description from the patent application of April 16, 1878, is glued to the back of the tag. The tag is attached to the handle with a red ribbon.

L. Leland Locke, a New York mathematics teacher and historian of mathematics, collected this patent model and intended it for the Museums of the Peaceful Arts in New York City. When that institution encountered financial difficulties in 1940, Locke gave a collection of objects, including this model, to the Smithsonian Institution.

For production models of this instrument, see MA*313751, MA*316575, and 1998.0046.01.